Perennial Weed Management in Row Crops and Perennial Forages

Presented by the PSU Weed Science team:

Dwight Lingenfelter, Extension Associate

Bill Curran, Professor of Weed Science

Annie Klodd, Extension Associate

Perennial Weeds

• Generally live more than two years

• Can reproduce in several ways, beyond just seeds

• Store energy in vegetative structures

Two types:

• Herbaceous

• Woody

Dupont.ca

Progressiveforage.com

Bill Johnson

Types of perennial weeds

Herbaceous- die back every season, then come back next year

Simple- emerge from same

taproot system every year.

- often rely on seeds for reproduction.

Creeping- reproduces and

spreads via vegetative structures

CREEPING

Types of perennial weeds

WoodyContinue growing from same “woody” structure year after year

Some reproduce via vegetative structures (creeping)

Some do not creep - simple

Common problem perennials of the Northeast

Simple Creeping Woody

Chicory Bindweed Brambles

Dandelion Canada thistle Autumn olive

Dock species Groundcherry Multiflora rose

Plantain Hemp dogbane Poison ivy

Pokeweed Horsenettle Sumac

White cockle Ironweed Tree-of-heaven

Wild four-o’clock Japanese knotweed Virginia creeper

Johnsongrass

Milkweed

Mugwort

Quackgrass

Smooth bedstraw

Wirestem muhly

Yellow nutsedge

Perennial Vegetative Structures

Structures that:

- allow the plant to reproduce and grow

- store energy from year to year

Quackgrass rhizomes

Johnsongrass stolon & rhizomes

Stolons - above-ground horizontal stems that root at the nodes to spread the weed.

Rhizomes - below-ground thickened stems that grow horizontally in the upper soil layers.

Yellow nutsedge rhizomes/tubers

Hemp dogbane root buds

Tubers - enlarged rhizomes with compressed internodes located at the ends of rhizomes.

Budding roots - modified roots that can store carbohydrates and grow vertically and horizontally.

Wild garlic bulbs

Jerusalem artichoke tubers

Bulbs – modified leaf tissues that store carbohydrates. Located at the base of the stem, at or below the soil line.

Tubers - enlarged rhizomes with compressed internodes located at the end of ends of rhizomes.

Vegetative Structures are the:

“Energy Reserves”

Energy, or carbohydrate, storage found in vegetative structures

Perennial Broadleaf Energy Reserves:

April May June July August Sept. Oct.

Sto

red E

nerg

y

Canada thistle

“Bud to Bloom”High!

Low…a lot has been moved aboveground.

Hemp dogbane

Dandelion

Milkweed

Importance of Seed Production

• Seed production may be important for spread - new infestations

• Transport within and between fields and longer distances

• Longer lived than vegetative structures• Good news - small plants from seed may

be susceptible to standard controls

Vegetative and Seed Production for Selected Perennials –Prevent seed production

Weed Vegetative Seed

Canada thistle Rhizomes Fairly important

Dandelion Taproot buds Very important

Hemp dogbane Creeping roots Important

Johnsongrass Rhizomes Very important

Nutsedge Tubers Not important

Quackgrass Rhizomes Fairly important

Small plants from seed may be susceptible to standard controls

Herbicide JG HDB MW CT PKW HN

Atrazine 22 100 85 99 84 96

Authority 41 100 64 73 90 65

Canopy 80 100 97 99 96 89

Dual 33 69 75 30 16 28

Lorox 27 58 32 88 36 48

Prowl 38 44 56 34 28 26

Python 76 81 80 98 92 81

Scepter 86 81 77 91 86 80

Metribuzin 76 100 99 100 88 96

Effect of soil applied herbicides on perennial seedlings (% control in greenhouse) –M. VanGessel, Univ. of Delaware

Perennial weeds are a symptom ofmanagement

• Undisturbed habitats

• Grass hay and pasture

• Alfalfa and other perennial legumes

• No-till/reduced-till systems

• Roadside habitats

• Turfgrass/lawns

USDA NRCS

Univ. of TN

Annual tillage –Annual weeds, creeping perennials

Photo courtesy of S. Culpepper, University of Georgia.

Reduced-till –Simple perennials & small-seeded annuals

Photo: S. Culpepper, University of Georgia

Pokeweed Pigweed (small-seeded annual)

Photo: Ohio State Weed Guide

White cockle roots

No-till fields & pastures –Woody & herbaceous perennials and biennials

Autumn Olive in pasture. Photo: WV Univ.

Photo: WV Univ.

Perennial Weed Biology Summary

Lifecycle • Live more than two years• Herbaceaous [simple, creeping], and woody• Vegetative structures: Reproduction & energy

storage.

Plants can be targeted when energy reserves are lowest (bud-bloom & fall)

Seed production is still important for some simple perennials

Perennial weeds depend on land management

Next up:Successful management of

perennial weeds

Row crops

Grass hay and pasture

Alfalfa

Management is most successful with an integrated approach

Prevention• Stop weeds before they become established

Cultural• Includes crop rotation, competitive crop varieties, soil fertility,

crop competition, planting density, planting date, routine field scouting, ensiling weed-infested crops, etc.

Mechanical• Use of physical techniques such as hoeing, mowing, plowing,

cultivating, digging, mulching

Biological• Involves the use of other living organisms such as insects, diseases,

or livestock to control certain weeds

Chemical• Herbicides - convenient, economical, effective when used in

combination with other tactics

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Integrating tactics for perennial weed management

Selecting tactics:• Design program based on what is best for the particular

weed species and farm operation

Consider weed biology:• Target perennials during certain times of year for best

control

Fall

Early summer

Cultural –Crop Rotation

Cultural tactics: Crop management decisions that improve weed control

Selecting crop rotations to aid in perennial weed mgmt:• Breaks weed lifecycles – stops certain weeds from dominating

• Adds options for tillage & mowing • Mowing - Perennial forages and winter grains

• Tillage - Summer annual crops

• Adds herbicide options

• Small grains create better herbicide timing (early summer, fall)

Perennial Broadleaf Susceptibility

April May June July August Sept. Oct.

Root Energy or Susceptibility to Systemic Herbicide

“Bud to Bloom”

ReservesSusceptibility

Movement to roots

Mechanical –Tillage and Perennial Weeds

• Perennial weeds are more common in no-till (undisturbed) areas

• Tillage disrupts vegetative growth – esp. simple & woody perennials

• Deep tillage more effective than shallow

• Fall tillage better than spring, but carries environmental concerns

Follow tillage with winter cover crop

Part of integrated strategy:

• Chisel plow and disking alone can increase spread of creeping perennials

• Tillage alone is generally inadequate and should be used selectively and with other tactics

In no-till fields:

If not tilling, perennial weed management relies more on cultural tactics, herbicide, and possibly

biological control like grazing.

Moldboard Plow

High Residue Cultivator

Chisel Plow

Vertical tillage

Most potential for perennial control

Tillage – good or bad for thistles?

• Mold board plow will bury roots deep

• Chisel plowing in fall will expose taproots• Good or bad result depends on timing.

X Do not chisel plot thistle right before planting a crop –taproots will re-sprout along with the crop

Could chisel plow before winter, exposing roots to freezing to kill them

Mechanical –Mowing• Removes tops to prevent seed formation

• Depletes underground food reserves

• Aids growth of desirable vegetation –grasses/legumes

Challenges:

• Not effective on some species –simple perennials

• Repeated mowing necessary for complete control – often not practical except in alfalfa

• Certain livestock grazing practices can target specific perennials

• Examples:• Goats consume poison ivy and multiflora rose

• Sheep in fall, on Canada thistle, followed by fall herbicide

• Intensive, low-frequency cattle

• Carefully consider challenges

Biological-Livestock grazing on perennials

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Herbicides and Perennials

• Soil-applied – may have some impact on seedlings, but rarely established plants

• Foliar applications – necessary for vegetative control

• Timing is very important, but doesn’t always line up with crop

• June-early July & fall

Control of Hemp Dogbane depends on application timing and rate: Roundup – year after application

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Vegetative Bud Early Flower Full Flower

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J. Doll, U of Wisc.

Pokeweed: Effect of glyphosate application timing on control

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K. Patches, Penn State (2012/2013)

Crop Rotation and Herbicide Timing – when to apply

• 1 to 3 weeks prior to planting or after harvest:

• Apply systemic herbicide to actively growing perennials

• Fits better with fall-seeded small grain or alfalfa planting or…

• After winter wheat harvest

Example – Best Case ScenarioIntegrate Cultural, Mechanical, Chemical tactics

Early summer: Follow ryelagewith competitive annual forage

Early July: harvest topgrowth. Allow forage & weeds to regrow

Mid-August: harvest topgrowth. Allow forage & weeds to regrow

Late summer: Apply systemic herbicide (2,4-D + dicamba)

Greencoverseed.com

• Combines crop competition (Cultural), mowing (Mechanical), and herbicide (Chemical)

Perennials of Row Crops

• Common problems: Canada thistle, pokeweed, dandelion, horsenettle, hemp dogbane, Johnsongrass, others

• Simple and creeping herbaceous

• Most problematic in no-till – less disturbance

• Can be competitive in corn, soybean, and small grains

• Suppression often depends on herbicides

Table 2-12. Herbicide effectiveness on perennial broadleaf weeds in corn2017 Mid-Altlantic Field Crop Weed Management Guide

Table 4-12. Effectiveness of postemergence herbicides on perennial broadleaf weeds in soybean (based on seasonal control)

2017 Mid-Atlantic Field Crop Weed Management Guide

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Glyphosate important for pokeweed control in soybean

(visual rating), 12WAA, 2012/2013.

Perennials Weeds of Grass Hay and Pasture• Common problems: Canada thistle,

horsenettle, smooth bedstraw, dock species, multiflora rose, others

• Simple, herbaceous, and woody

• Presence often depends on grazing and mowing management and age of stand

• More herbicide options

• Control dependent on mowing, fertility mgt., and herbicides

Table 6-11. Relative effectiveness of grass pasture, hay, and CRP grassland herbicides.2017 Mid-Atlantic Field Crop Weed Management Guide

Perennial Weeds of Alfalfa

• Common problems: dandelion, plantain, dock species, white cockle, others

• Mostly simple perennials that tolerate mowing

• Presence often depends on mowing management and age of stand

• Control depends on mowing, herbicide, and crop rotation

Table 6-5. Relative effectiveness of herbicides on weeds and crop tolerance in legume forages.

2017 Mid-Altlantic Field Crop Weed Management Guide

Roundup Ready AlfalfaExtension Publication: Agronomy Facts 65

http://extension.psu.edu/publications

• Benefits: good weed control, wide harvest intervals, greater potential for no-till, other

• Challenges: alfalfa-grass mixtures, concern for resistant weeds, more expensive seed

• Refer to fact sheet for more details